The invention relates to a vacuum pump, in particular for brake booster systems in motor vehicles, according to the preamble of claim 1.
Vacuum pumps of the type addressed here are known. They have a rotor consisting of metal, usually sintered metal, which can be set in rotation by a drive shaft. The rotor disposed in a housing is in engagement with a blade which slides along a contour ring. The rotor consists of several individual parts which are removably connected to one another. It has been shown that the rotor has great inertia due to its weight, whereby the power consumption of the vacuum pump is undesirably high. The rotor furthermore has a massive and expensive structure.
It is thus the objective of the invention to provide a vacuum pump of the type stated initially which does not have these disadvantages.
For the realization of this objective a vacuum pump is proposed which has the features stated claim 1. It is distinguished by the fact that the rotor consists of plastic and is formed as one piece. The rotor can be produced in a simple and cost-effective manner, for example in the injection-molding process, and has, in comparison to the prior-art rotors, a lighter weight. Due to the unipartite form of the rotor, a compact structure is possible so that the space needed for the vacuum pump can be reduced. The power consumption of the vacuum pump is relatively low due to the low inertia of the rotor.
An exemplary embodiment of the vacuum pump is preferred in which the rotor has at least one cavity open at the edge. In case of the preferred production of the rotor in the injection-molding process the cavity or cavities can be produced in a simple manner by the laying into the injection mold of correspondingly formed cores. By the introduction of cavities in the rotor, thin walls can be realized, for example outwards up to a slot in which the blade can be displaced. Further more, the weight of the rotor, which is already lighter because it consists of plastic, can be reduced.
An exemplary embodiment of the vacuum pump is also preferred which is distinguished by the fact that the curve of wall thickness of the rotor is continuous or essentially continuous. That is, the transition between two wall areas having a different thickness is uniform and has no clear discontinuities in wall thickness.
An exemplary embodiment of the vacuum pump is also preferred in which the rotor has at least two cavities disposed next to one another, said cavities being separated from one another by a rib. The rigidity of form of the rotor is increased further by the ribbing. The rib formed between two cavities is preferably thinner than the other wall of the rotor. Thereby points of incidence in the transitional area of the rib and a wall of the rotor are avoided. In the case of a preferred exemplary embodiment the thickness of the rib or ribs lies in the range of 1.0 mm to 2.0 mm while the wall thicknesses of the rotor in comparison thereto then preferably lie in the range 1.5 mm to 3.0 mm.
A form of embodiment of the vacuum pump is also particularly preferred which is distinguished by the fact that the rotor has at least one closed wall running transversely or essentially transversely to the central longitudinal axis of the rotor. Thereby it can be insured that in the case of a rotor having a cavity no air can reach from the drive side through the rotor into the vacuum pump. Therefore no additional seals are necessary.
In the case of a preferred exemplary embodiment of the vacuum pump it is provided that the rotor has an elastic drive element working together with a drive shaft. Through the drive element, which is in engagement with the rotor directly or via a coupling, the torque spikes or oscillations transmitted from the drive shaft coupled to, for example, the internal combustion engine of a motor vehicle, as, for example, occur in the case of direct-injection motors, are damped so that a break of the motor is avoided with high reliability.
In the case of an advantageous form of embodiment the drive element consisting, for example of metal, preferably spring metal, is formed as a torsion rod which is twisted under the torque conducted. Thus, for example in the case of an exemplary embodiment in which the rotor is driven by the internal combustion engine of the motor vehicle, any torque spikes, such as occur, for example during the cold start of the vacuum pump and/or in connection with direct injection motors, can be smoothed and clearly reduced.
Finally, an exemplary embodiment of the vacuum pump is also preferred which is distinguished by the fact that the drive element projects into a slot in the drive shaft and is displaceably guided in it. Thereby a shift of the axis between the vacuum pump and the drive shaft can be compensated in an advantageous manner without a coupling being needed for that purpose. A compensation of a shift of the axis perpendicularly to the slot can be compensated in the case of a fixed connection of the drive element to the rotor by the bending of the drive element in its elastic range. If the drive element is loosely connected to the rotor so that it can execute a relative motion with respect to the rotor, then a shift of the axis perpendicularly to the slot can be compensated by a tilting of the drive element.
According to an extension of the invention it is provided that the rotor can be driven with the aid of the internal combustion engine of a motor vehicle. In the case of another exemplary embodiment of the vacuum pump the rotor can also be driven by a motor, in particular an electric motor, when the vacuum pump is used in a motor vehicle, for example in connection with a brake booster system of the motor vehicle. The motor can, for example, also be operated hydraulically or pneumatically. In the case of an additional variation of embodiment the rotor is optionally drivable by the internal combustion engine or the motor.
Additional advantageous forms of embodiment follow from the subordinate claims.